Vidicon target plate having a drift field region surrounding each image element

ABSTRACT

A semiconductor device, particularly a camera tube having a target plate for converting a radiation picture into electric signals, the target plate comprising a mosaic of radiationsensitive elements, and being furthermore doped in such manner that the charge carriers produced by radiation are conveyed to the desired element by incorporated electric fields.

Unite States Patent Hart Mar. 14, 1972 [54] VIDICON TARGET PLATE HAVING A [56] References Cited i ig gg UNITED STATES PATENTS 3,403,284 9/1968 Buck ..3l5/H [72] Inventor: Pen] Anton Herman Hart, Emmasingel, 3,458,782 7/1969 Buck at a] Emdhoven, Netherlands 3,298,880 [/1967 Takagi et a]. ..148/191 F'l N 14 1969 [22] 1 ed M Primary Examiner-John W. l-luckert [21] App].No.: 876,759 Assistant ExaminerMartin l-l. Edlow Attorney-Frank R. Trifari [30] Foreign Application Priority Data 57] ABSTRACT Nov. 27, 1968 Netherlands ..6816923 A semiconductor device particularly a camera tube having a target plate for converting a radiation picture into electric [52] US. Cl ..317/235 R, 317/235 N, 317/235 AM, Signals, the target plate comprising a mosaic of radiatiomsflm 317/235 AN sitive elements, and being furthermore doped in such manner [51] Int. Cl ..H0ll 17/00, H011 15/00 that the charge carriers Produced by radiation are conveyed to [58] Feld Search 17,235 235 the desired element by incorporated electric fields.

14 Claims, 4 Drawing Figures i7 21 16 3 1 l z. j

PAIENIEDMARM I972 3,649,889

SHEET 1 [1F 4 INVENTOR.

PAUL A.H. HART AGT PATENTEB 1 972 3. 649.889

INVEN PAUL A.H. HA

AGEN

PATENTEDHAR 14 1972 SHEET 3 BF 4 INVENTOR. PAUL A. H. HART AGENT PATENTEDHAR 14 I972 3, 649 889 sum u OF 4 fan 1 H! f g, i g L 47 INVENTOR.

PAUL A.H. HART BY 2% AW AGENT VIDICON TARGET PLATE HAVING A DRIFT FIELD REGION SURROUNDING EACH IMAGE ELEMENT The invention relates to a semiconductor device having a semiconductor body with a substrate region of one conductivity type provided with a connection conductor, of which semiconductor body a surface is at least partly covered with an insulating layer and comprises a radiation-sensitive mosaic of substantially identical radiation-sensitive elements for converting a radiation pattern into electric signals, said elements being arranged regularly and each forming a rectifying junction with the substrate region in an aperture in the insulating layer.

The invention furthermore relates to a method of manufacturing such a device.

Imaging devices of the above-mentioned type are known and may be used for converting radiation images of various natures. for example, for reading punched cards or punched tapes. According to a very important use, they form target plates and image pickup tubes with target plates, respectively, for video signals, see, for example, I967 International Solid State Circuits Conference" Digest of Technical Papers, Feb. 1967, pp. l28l29. In these papers a device is described having a semiconductor plate with a radiation-sensitive mosaic of diodes at one surface, one side of which is set up at a fixed potential via a connection conductor provided on the semiconductor plate, the other side of diodes being charged periodically by an electron beam to a potential such that the diodes are biased in the reverse direction.

When the semiconductor plate is irradiated with a locally different intensity, for example by projection of a picture on the plate, charge carriers are generated in the plate with a density which depends upon the local radiation intensity. As a result of this the diodes are discharged to a greater or lesser extent and hence the radiation pattern is converted into a charge pattern. During the subsequent passage of the electron beam, the fully or partly discharged diodes are charged again, current pulses occurring in the said connection conductor the value of which depends upon the extent of discharge of the various diodes. These current pulses can be detected, for example, as voltage variations across a load resistor incorporated in the connection conductor.

In order to obtain a good definition it is necessary that the radiation-sensitive elements be small and that the charge carriers generated at a given place be collected by the radiationsensitive element corresponding to said place, and that they do not reach an adjacent element or the intermediate semiconductor surface. In order to achieve this, for example, the mosaic elements may be placed together as close as possible. Furthermore, when the radiation is incident on the sur face of the target plate opposite to the mosaic element, it will be endeavored to make the latter as thin as possible.

In addition to the fact that technically it is not well possible to give the semiconductor plate any arbitrary thinness, the plate must have a given minimum thickness which lies in the order of from to I00 .1m. so as to maintain a sufficient sensitivity at larger wavelengths. Moreover, it is in general objectionable to place the radiation-sensitive elements very close together, since as a result of this the capacity of the target plate can become undesirably high which reduces the speed of the target plate. A further drawback is that when many very small elements placed close together are used, the overall leakage current (dark current) becomes comparatively large.

So if the speed of the target plate is to be increased, the plate will have to be made smaller or, when the area of the target plate remains the same, the mosaic elements will have to be spaced further apart. In both cases, however, the definition will decrease.

It is the object of the invention to provide a new construction of a radiation-sensitive semiconductor device of the type described in which a high switching speed can be obtained, while nevertheless a high definition can be obtained.

The invention is based inter alia on the recognition of the fact that by a suitable doping profile incorporated in the semiconductor body, the collection of charge carriers produced locally by radiation by adjacent elements or the flowing away of charge carriers to the semiconductor surface situated between the elements is prevented, while said carriers can also be conveyed to the corresponding desired element.

Therefore, according to the invention a radiation-sensitive semiconductor device having a semiconductor body with a substrate region of the one conductivity type provided with a connection conductor, of which semiconductor body a surface is at least partly covered with an insulating layer and comprises a radiation-sensitive mosaic of substantially identical radiation-sensitive elements for converting a radiation pattern into electric signals, said elements being arranged regularly and each forming a rectifying junction with the substrate region in an aperture in the insulating layer, is characterized in that such an inhomogeneous doping concentration is incorporated in the substrate region that, at least in that part of the substrate region remote from the mosaic which is bounded by the common tangential plane at the rectifying junctions, an electric field is present in all directions reckoned from the said rectifying junction, under the influence of which field minority charge carriers in the substrate region will move in the direction of the rectifying junction.

Due to the doping profile or gradient provided according to the invention, an electric field is incorporated in the structure, by which the minority charge carriers produced by irradiation cannot diffuse to adjacent elements or to the surface.

The device according to the invention inter alia has the important advantage, as compared with known devices, that the dimensions of the radiation-sensitive elements are no longer decisive of the capturing power, as a result of which the elements can be made much smaller than normally, which considerably reduces the capacity and the dark current.

The doping profile incorporated according to the invention can be realized in various manners, for example, by a doping concentration increasing omnidirectionally from the rectifyingjunction, in which said concentration variation can extend throughout the substrate region. According to an important preferred embodiment which can be realized technically in a simple manner, the rectifying junction is formed between a zone of the radiation-sensitive element and a first substrate zone of the one conductivity type which has a lower doping concentration than a second substrate zone of the one conductivity type which within the semiconductor body substantially entirely surrounds the part of the first substrate zone bounding the rectifying junction.

It is to be noted that the second substrate zone substantially entirely surrounds the part of the first substrate zone within the semiconductor body bounding the rectifying junction in the sense of the invention, if the second substrate zone extends between two radiation-sensitive elements at least up to the common tangential plane determined by their rectifying junctions. However, the second substrate zone preferably extends between the elements up to the semiconductor surface, as a result of which a separation between the radiation-sensitive elements is obtained which is as complete as possible. The doping concentrations will advantageously be chosen to be so that the second, more highly doped substrate zone between the radiation-sensitive elements has such a high doping concentration at least at the surface that no inversion channel can be formed there. In the case of comparatively high-ohmic material, such an inversion channel can actually be formed easily between the semiconductor material and the insulating layer, usually an oxide layer. As a result of this, leakage paths can be formed between the radiation-sensitive elements. In order to prevent this, a surface doping of from 10 to 19' atoms per cc. is generally sufficient in the case of silicon, for example.

The said rectifying junction may consist of a metal-semiconductor junction. For example, the radiation-sensitive elements may consist fully or partly of Schottky diodes. However, the rectifying junction is preferably formed by a PN-junction between a zone of the opposite conductivity type associated with the radiation-sensitive element and the substrate region.

The said first substrate zone may be, for example, a substantially homogeneously doped zone having a lower doping than a second substrate zone which surrounds the first substrate zone. A more or less abrupt doping junction is then formed between the said substrate zones. This junction and the electric field associated therewith prevents the capturing of the charge carriers generated by the radiation by an adjacent radiation-sensitive element. According to an important preferred embodiment, however, the first substrate zone has a doping concentration which decreases continuously from the second substrate zone to the rectifying junction. As a result of this a drift field is incorporated in the first substrate zone in a manner analogous to that of a drift transistor, as a result of which the minority charge carriers produced by radiation are directed in the direction of the desired radiationsensitive eiement. The structure of the device is preferably chosen to be so that the doping concentration of the first substrate zone reckoned or measured from thejunction between the first and the second substrate zone, decreases more slowly along the insulating layer to the rectifying junction than from the remaining part of the junction between the first and the second substrate zone to the rectifying junction, so that the rectifying junction is situated in a region of a lower doping which narrows towards the surface, resulting in that the said effects are even intensified The distance from the rectifying junction to the second substrate zone is advantageously chosen to be maximally equal to the average diffusion length of the minority charge carriers in the first substrate zone. As a result of this the optimum capturing of charge carriers in the radiation-sensitive elements is ensured, since the number of charge carriers which recombine before reaching the rectifying junctions becomes negligibly small.

Schottky diodes, PN-diodes, transistors, PNPN elements or other radiation-sensitive structures may be used as radiationsensitive elements. The device becomes most simple when the radiation-sensitive elements consist of diodes. According to another preferred embodiment, the radiation-sensitive elements consist of phototransistors the base-collector junction of which is formed by the said rectifying junction. At the expense of a slightly more complicated structure, the advantage of an extra amplification is obtained.

If the rectifying junction is a PN-junction, said junction will in most of the cases be formed preferably between an N-type substrate region and a P-type zone, since the scanning electron beam generally will charge the radiation-sensitive element negatively. As a result of secondary emission at the semiconductor surface, however, a positive charge may occur in circumstances. This might occur also, for example, by using a bundle of positively charged particles, for example, positive ions, instead of an electron beam. It is obvious that, when such a positive charge is used, a P-type substrate will be used which forms a PN-junction with an N-type zone of the radiation-sensitive element.

The invention is of particular interest in the case in which the device is an image pickup tube comprising an electron source which is capable of producing an electron beam with which a target plate can be scanned which is formed by the said semiconductor body which is provided with a radiationsensitive mosaic.

The device described can be manufactured in various man ners. For example, a target plate of the type described can be manufactured, by starting from a plate-shaped substrate of the one conductivity type in which an impurity of the same conductivity type is diffused from one side throughout the surface, while this is done selectively from the other side in the form of a grating or grid in such manner that the regions diffused from both sides touch one another. The radiation-sensitive elements are then provided in or on the nondiffused remaining parts, which form trays oflower-doped material.

A particularly practical method of manufacturing a device according to the invention is characterized in that the starting material is a substrate of the one conductivity type in which cavities are provided at a surface by selective etching at the area of the radiation-sensitive elements to be formed after which a semiconductor iayer of the one conductivity type having a lower doping than the substrate is provided on said surface by epitaxial growing, after which the rectifying junction is formed in or on the parts of the epitaxial layer situated above the cavities and the further semiconductor zones associated with the radiation-sensitive elements are provided. If desirable, a heating of the body may be carried out after providing the epitaxial layer, so that the doping impurity diffuses from the substrate in the epitaxial layer, thus permitting to control at will the doping profile thereof. During the epitaxial growth also a certain out-diffusion generally takes place already. The epitaxial layer after growing is preferably ground down until the substrate between the cavities is reached, as a result of which regions of the epitaxial layer entirely separated entirely from each other remain in the cavities, in or on which regions the radiation-sensitive elements are provided, generally after an etching process, to form a crystal surface which is free from defects as much as possible.

According to another preferred embodiment according to the invention, an N-type substrate is used in which after growing at least the substrate is removed by means of an electrolytic etching method, so that no radiation absorption can occur in the highly doped substrate.

Another particularly suitable method according to the invention is characterized in that the starting material is a substrate of the one conductivity type which is provided at a surface with a masking layer in which windows are etched locally, after which the doping impurity is partly diffused out of the substrate via the windows by heating, to form lower-doped zones below the windows, after which the rectifying junction is formed in or on said zones and the further semiconductor zones associated with the radiation-sensitive elements are provided. The degree of out-diffusion determines the doping profile of the first substrate zone.

When the semiconductor body is destined for radiation incidence on the side remote from the radiation-sensitive mosaic, the semiconductor body, after providing the radiation-sensitive elements, is preferably reduced in thickness on the side remote from the elements by removing material to an overall thickness which is maximally equal to the absorption length in the substrate of the radiation to which the elements are sensitive.

In order that the invention may be readily carried into effect, a few embodiments thereof will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic cross-sectional view ofa device according to the invention,

FIGS. 2, 3, 5, 6, 7 and 8 are diagrammatic cross-sectional views of the device shown in FIG. 1 in successive stages of manufacture,

FIG. 4 is a plan view of the device shown in FIG. 1 in the stage of manufacture which is shown in the cross-sectional view of FIG. 5 taken on the line V-V,

FIG. 9 is a diagrammatic cross-sectional view of another device according to the invention,

FIGS. 10 and 11 are diagrammatic cross-sectional views of further embodiments of the device according to the invention,

FIGS. 12 and 13 are diagrammatic cross-sectional views of still another embodiment of the device according to the invention in successive stages of manufacture, and

FIG. 14 is a diagrammatic cross-sectional view of a device according to the invention in the form of an image pickup tube.

For clarity, the Figures, particularly the direction of thickness, are not drawn to scale. Corresponding components in the drawings are referred to by the same reference numerals.

FIG. 1 is a diagrammatic cross-sectional view of a part of a semiconductor device according to the invention. The semiconductor device comprises a plate-shaped semiconductor body of silicon having an N-type substrate region 3,4 pro vided with a connection conductor 2. A radiation-sensitive mosaic consisting of mutually equal radiation-sensitive diodes 7,4 each having a rectifying PN-junction 6 between a P-type zone 7 and a first N-type substrate zone 4 is provided on a surface 5 of the silicon plate. Said first substrate zone 4 is lower doped than the region 3, the second substrate zone, which extends between the diodes up to the semiconductor surface 5 and which, at each of the diodes, fully surrounds the zone 4 within the semiconductor body. The surface 5 between the diodes 7,4 is covered with a silicon oxide layer 12.

The second substrate zone 3 has a phosphorus doping concentration of 10 atoms per cc. The first substrate zone 4 has a doping concentration which continuously decreases from a value of IO phosphorus atoms per cc. at the area of the junction between the zones 3 and 4, to a value of 10 atoms per cc. at the area of the rectifyingjunction 6.

As a result of the inhomogeneous doping or gradient described, an electric drift field is present in the substrate region 3,4, reckoned or measured from every junction 6 in all directions, which field is directed towards the relativejunction 6 and as a result of which holes in the substrate region will move in the direction of the junction 6.

In accordance with the above, the second substrate region 3 has a doping of 10 atoms per cc. at the surface 5. This is generally sufficient to prevent the formation of an inversion channel at said surface which might form a leakage path between the diodes.

The device shown in FIG. 1 can be manufactured, for example, as follows. Starting material (see FIG. 2) is an N-type silicon plate 3 having a diameter of 25 mm., a thickness of 200 ,um. and a phosphorus doping of 10" atoms per cc., which plate is oriented so that its main surfaces extend substantially parallel to the l)-crystallographic plane.

One of the main surfaces of said silicon plate is polished and etched so that the surface shows a crystal structure which is as perfect as possible. This surface is then oxidized at 1,l00 C. in moist oxygen until an oxide layer 8, 0.5 ,u.m. thick, is obtained (see FIG. 3).

Square holes 9 of 27 um. X 27 pm. with a pitch of 30 pm. in the direction of the sides of the holes are provided in said oxide layer while using photoresist methods conventionally used in semiconductor technology (see FIG. 4 and the cross sectional view taken on the line V-V shown in FIG. 5). An etching treatment is then carried out with a mixture consisting of 250 gm. of KOI-I, 850 gm. of H 0 and 25 gm. ofisopropanol for approximately 15 minutes, during which (see FIG. 6) cavities having a depth of 13 um. are formed in the silicon. As a result of the 100) orientation of the silicon plate, the etching occurs substantially only in the direction of the thickness of the plate, while in the lateral direction practically no silicon is etched away below the oxide layer.

The oxide layer 8 is then removed by etching in hydrofluoric acid, and the layer 11 of N-type silicon having a phosphorous doping of 10 atoms per cc. is provided in a thickness 0f pm. by epitaxial growing on the surface and in the cavities 10 (see FIG. 7).

The epitaxial layer 11 is then ground down until the highly doped N-type substrate 3 is reached and etched so that mutually separated epitaxial regions 4 remain, (see FIG. 8). The silicon plate is then heated at l,200 C. for 3 hours in an atmosphere of oxygen saturated with water at 25. An oxide layer 12, 0.6 gm. thick, is formed (see FIG. 8) while at the same time phosphorus diffuses in the regions 4 from the N substrate 3, so that in said regions 4 a phosphorus concentration occurs which decreases from the substrate 3, in which, at the area of the broken line 13, the phosphorus concentration has reduced to 10 at./cc. This surface 13 of equal concentra tion is for the greater part parallel to the surface 5, and lies there approximately 2 pm. below said surface. As a result of the fact that the phosphorus atoms diffuse less easily in the silicon oxide than in the silicon, the surface 13, where the concentration is 10' atoms per cc., bends inwardly at the surface 5, so that the phosphorus concentration decreases more slowly along the oxide layer 12 than from the remaining part of thejunction between the zones 3 and 4.

Circular windows 14 (see FIG. 1), l0 ,um. diameter, are etched in the oxide layer 12, again while using known photoresist methods. Boron is diffused in a closed capsule via said windows in the conventional manner at l,l00, the source being silicon powder having a boron concentration of l0 atoms per cc., until the diffused P-type zones 7 (see FIG. 1) have been formed having PN-junctions at approximately 2 ,um. below the surface. Since the duration of this boron diffusion is much shorter than that of the preceding out-diffusion of phosphorus atoms from the zone 3 in the epitaxial zone 4, the phosphorus distribution in the epitaxial region 4 does substantially not vary during said boron diffusion. So the PN-junctions 6 are situated approximately at the level where the phosphorus concentration decreasing from the substrate has reduced to the original donor concentration of the epitaxial layer 11.

The distance from the PN-junctions 6 to the substrate region 3 is in this example everywhere smaller than 50 um., which is smaller than the average diffusion length of holes in the region 4, so that optimum capturing of charge carriers by the junctions 6 is achieved.

The further finishing of the target plate depends upon the way in which it is used. When the electron beam for scanning the diodes and the light beam for forming the radiation picture are both incident on that side of the target plate where the diodes are situated, which is possible, for example, by causing the electron beam and the picture-forming light-beam to be incident at different angles on the target plate, it is sufficient to provide an electrode layer 2 on the whole surface of the target plate remote from the diodes (see FIG. 1). When the light beam is incident on the target plate from the other side it is recommended to reduce the thickness of the target plate by grinding and etching from the side remote from the diodes, to a total thickness which is at most equal to the absorption length in the substrate of the radiation to which the elements are sensitive, in the present example, for example, to a thickness of 20 pm. On the surface where the light beam is incident, an annular contact is provided along the edge, in which, if desirable, the target plate may be secured to a radiation-permeable support so as to increase the rigidity.

According to a variation of the method described, an N- type zone 15 can be selectively diffused in the P-type zones 7 in the conventional manner after providing said zones, the depth of penetration being, for example, 1 am, see FIG. 9. The radiation-sensitive elements are then formed by phototransistors 15, 7, 4 the junction 6 of which forms the col lector-base junction.

According to a variation the method described may also be carried out while omitting the grinding down of the epitaxial layer 11. A slightly different structure is then obtained. A detail of this structure having two diodes 16,4 and 17,4 is shown in FIG. 10. The second substrate zone 3 does not extend up to the semiconductor surface, but does extend to beyond the common tangential plane 18, which is determined by the rectifying junctions 19 and 20. According to a further preferred embodiment, the substrate 3, as well as a part of the highly doped part of the layer 11 formed by out-diffusion can be removed in this case, so that the structure of FIG. 11 is obtained, for example by an electrolytic etching treatment as described in the published Dutch Pat. No. 6,703,013 applied to the side of the silicon plate remote from the diodes. During this electrolytic etching treatment, material is removed to a doping concentration of approximately 10 at./cc., while the remaining part of the layer 11 is not attacked. The doping boundary with a concentration of 10 cm? is shown in FIG. 10 by the broken line 21, and the N-type silicon is removed approximately up to said border line (see FIG. 11). The remaining part of the regions 4 maintains a doping gradient. As a result of this, according to the invention, a drift field is present in the parts 4 of the substrate region remote from the radiation-sensitive mosaic which parts are bounded by the common tangential plane 22 at the PN-junctions l9 and 20,

calculated from said junctions in all direction, which drift field is oriented towards said junctions. Under the influence of this drift field, holes will move to the junctions l9 and 20. The structure of FIG. 1] has the advantage that radiation absorption in the substrate 3 is now avoided entirely which is of importance particularly for the shorter wavelengths. However, the structure is not very rigid mechanically and will therefore preferably be provided on a support.

Another method of manufacturing a device according to the invention will be described with reference to FIGS. 12 and 13. As in the preceding example, the starting material is an N-type silicon plate 31 (see-FIG. 12) diameter 25 mm, thickness 200 am., phosphorus concentration 10 atoms per cc. One of the main surfaces of said plate is again polished and etched, after which oxidation is carried out in moist oxygen at l,l until an oxide layer 32 of 0.5 m. thickness is obtained.

Circular windows 33, 6 [.Lm. diameter, 20 ,um. pitch, are etched in said oxide layer in mutually perpendicular directions so that a structure is obtained which is diagrammatically shown in the cross-sectional view of FIG. 11.

The silicon plate is then heated at a temperature of l,l50 for 150 hours in an evacuated quartz ampul in the presence of low-doped silicon powder (doping 10 atoms per cc. During this heating phosphorus atoms diffuse out of the plate outwards through the windows 33. As a result of this, lowerdoped regions 34 (see FIG. 11) are formed in the plate, in which regions the concentration increases from the surface to a value of 5. atoms per cc. at the area of broken line 35 at approximately 7 pm. below the surface.

Boron is then diffused via the windows 33 to a depth of 1 am, so as to form the P-type zones 36, see FIG. 13. At this depth, the phosphorus concentration is approximately 10 atoms per cc. The diodes 36,34 with the PN-junctions 37 form the radiation-sensitive mosaic.

An advantage of this method is that an epitaxial growth and an extra orientation step are not necessary, but on the other hand, a rather long out-diffusion time is necessary.

The further finishing of the target plate is effected in the same manner as in the first example.

FIG. 14 is a diagrammatic cross-sectional view of an image pickup tube according to the invention having a target plate of the above-described type. This image pickup tube comprises an electron source in the form of an electron gun 41 which can produce an electron beam with which the target plate 42 can be scanned by the deflection of the electron beam by means of a conventional system of coils 43. Electrons originating from secondary emission are collected by a grid 44. The lens 45 forms a radiation picture or image on the target plate 42 via the glass plate 46. The edge of the target plate comprises an annular connection contact 48 on the side remote from the radiation-sensitive diodes 47, which contact, in the operating condition, is connected to the positive terminal of a voltage source 50 via a resistor 49, the negative terminal being connected to the electron source 41. The diodes are charged by the voltage source 50 via the electron beam, and then discharged fully or partly by the incident radiation. The current signals obtained by the recharging of the diodes during the next passage of the electron beam can be derived, for example, at the terminals 51 and 52 via the resistor 49.

It will be obvious that the invention is not restricted to the examples described, but that many variations are possible to those skilled in the art without departing from the scope of the invention. On particular, the scanning of the radiation-sensitive mosaic may be effected in circumstances by means other than an electron beam. For example, a separate connection conductor can be provided on each of the radiation-sensitive elements on the side of the mosaic, via which conductor the charging of the elements can be effected. Radiation-sensitive elements other than diodes or transistors, for example, PNPN structures, may also be used while the device according to the invention can be manufactured also in manners differing from those described above. In addition to silicon, other semiconductor materials, for example, germanium or Ill-V compounds, may be used, while the various semiconductor zones may be constructed from mutually different semiconductor materials.

What is claimed is:

1. An imaging device comprising a semiconductor body, said body comprising a substrate region of one type conductivity having a major surface, an insulating layer on at least part of the major surface and having an array of apertures, said body having adjacent the major surface and under the insulating layer apertures an array of spaced imaging elements each forming with the adjacent substrate portion a rectifying junction, said rectifying junctions being spaced from one another and each having a portion tangential to an imaginary common plane which extends generally parallel to the major surface, the substrate regions adjacent each rectifying junction, at least on the side of said imaginary plane remote from the major surface, each having a gradient of concentration of impurities forming the said one type conductivity which increases in concentration from the rectifying junction radially in all directions into the substrate thereby to produce in the substrate a drift field extending from each junction in a direction causing minority carriers when generated in the body to be attracted toward the nearest junction.

2. An imaging device as claimed in claim 1 wherein each of the rectifying junctions is formed between a zone of an imaging element and a first substrate zone of the one type conductivity which has a lower one-type forming impurity concentration than a second substrate zone of the one type conductivity which within the semiconductor body substantially entirely surrounds the part of the first substrate zone bounding the rectifying junction.

3. An imaging device as claimed in claim 2, wherein the second substrate zone extends between the imaging elements up to the said major surfacev 4. An imaging device as claimed in claim 3, wherein the second substrate zone extending between the elements has such a high impurity concentration at least at the major sur face that no inversion channel can be formed there.

5. An imaging device as claimed in claim 2 wherein the first substrate zone has an impurity concentration which decreases continuously from the second substrate zone to the rectifying junction.

6. An imaging device as claimed in claim 5 wherein the impurity concentration in the first substrate zone measured from the junction between the first and the second substrate zones, decreases more slowly along the insulating layer than from the remaining part of the saidjunction.

7. An imaging device as claimed in claim 2 wherein the distance from the rectifying junction to the second substrate zone is at most equal to the average diffusion length of minority charge carriers in the first substrate zone.

8. An imaging device as claimed in claim 1 wherein the rectifying junction is formed by a PN-junction between a zone of the opposite type conductivity associated with each imaging element and the substrate region.

' 9. An imaging device as claimed in claim 8 wherein the imaging elements comprise diodes.

10. An imaging device as claimed in claim 8 wherein the imaging elements comprise phototransistors having base and collector regions forming ajunction constituting the said rectifying junction.

11. An imaging device as claimed in claim 1 wherein the device is an image pickup tube comprising an electron source which is capable of producing an electron beam for scanning a target plate which is formed by the said semiconductor body.

12. An imaging device as set forth in claim I wherein the substrate region remote from the major surface has a substantially uniform impurity concentration, the said impurity concentration gradient existing only in the immediate vicinity of the said rectifying junctions which lie adjacent the said major surface.

13. An imaging device as set forth in claim 12 wherein the substrate is N-type with an impurity concentration of about 223 UNITED STATES PATENT OFFICE QERTINCATE m CORRECTIGN Patent No. 3649889 Dated March 14, 1972 l PAUL ANTON HERMAN HART It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Title Page, Col. 1, there should have been added a line indicating the applicant's assignment to U. S. Philips Corporation, New York, New York.

Signed and sealed this 3rd day of October 1972.

(SEAL) Attest:

EDWARD MBFLETCHERJR, Q ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. An imaging device comprising a semiconductor body, said body comprising a substrate region of one type conductivity having a major surface, an insulating layer on at least part of the major surface and having an array of apertures, said body having adjacent the major surface and under the insulating layer apertures an array of spaced imaging elements eacH forming with the adjacent substrate portion a rectifying junction, said rectifying junctions being spaced from one another and each having a portion tangential to an imaginary common plane which extends generally parallel to the major surface, the substrate regions adjacent each rectifying junction, at least on the side of said imaginary plane remote from the major surface, each having a gradient of concentration of impurities forming the said one type conductivity which increases in concentration from the rectifying junction radially in all directions into the substrate thereby to produce in the substrate a drift field extending from each junction in a direction causing minority carriers when generated in the body to be attracted toward the nearest junction.
 2. An imaging device as claimed in claim 1 wherein each of the rectifying junctions is formed between a zone of an imaging element and a first substrate zone of the one type conductivity which has a lower one-type forming impurity concentration than a second substrate zone of the one type conductivity which within the semiconductor body substantially entirely surrounds the part of the first substrate zone bounding the rectifying junction.
 3. An imaging device as claimed in claim 2, wherein the second substrate zone extends between the imaging elements up to the said major surface.
 4. An imaging device as claimed in claim 3, wherein the second substrate zone extending between the elements has such a high impurity concentration at least at the major surface that no inversion channel can be formed there.
 5. An imaging device as claimed in claim 2 wherein the first substrate zone has an impurity concentration which decreases continuously from the second substrate zone to the rectifying junction.
 6. An imaging device as claimed in claim 5 wherein the impurity concentration in the first substrate zone measured from the junction between the first and the second substrate zones, decreases more slowly along the insulating layer than from the remaining part of the said junction.
 7. An imaging device as claimed in claim 2 wherein the distance from the rectifying junction to the second substrate zone is at most equal to the average diffusion length of minority charge carriers in the first substrate zone.
 8. An imaging device as claimed in claim 1 wherein the rectifying junction is formed by a PN-junction between a zone of the opposite type conductivity associated with each imaging element and the substrate region.
 9. An imaging device as claimed in claim 8 wherein the imaging elements comprise diodes.
 10. An imaging device as claimed in claim 8 wherein the imaging elements comprise phototransistors having base and collector regions forming a junction constituting the said rectifying junction.
 11. An imaging device as claimed in claim 1 wherein the device is an image pickup tube comprising an electron source which is capable of producing an electron beam for scanning a target plate which is formed by the said semiconductor body.
 12. An imaging device as set forth in claim 1 wherein the substrate region remote from the major surface has a substantially uniform impurity concentration, the said impurity concentration gradient existing only in the immediate vicinity of the said rectifying junctions which lie adjacent the said major surface.
 13. An imaging device as set forth in claim 12 wherein the substrate is N-type with an impurity concentration of about 1019 atoms/cc., and the concentration gradient runs from about 1019 to 1015 atoms/cc.
 14. An imaging device as set forth in claim 13 wherein portions of the N-type substrate with the impurity concentration of 1019 atoms/cc. extend to the major surface between the imaging elements and under the insulating layer. 